Gem having a stellar appearance

ABSTRACT

Disclosed is a gem ( 1 ) that has a stellar appearance. Said gem ( 1 ) comprises a crown ( 2 ) having a plurality of crown facets, including a first group ( 6 ) of crown facets that taper in the direction of a girdle ( 4 ) and extend at an angle (a) of 22.5°±3°, preferably 22.5°+2° from the girdle plane (E), and a second group ( 7 ) of crown facets that adjoin the girdle ( 4 ) by their large side and extend at an angle ( 13 ) of 34°±3°, preferably 34°±2° from the girdle plane (E). Also disclosed is an arrangement comprising a gem.

The present invention concerns a gem having a stellar appearance having the features of the classifying portion of claim 1 and an arrangement comprising such a gem.

Gems which are ground to a stellar shape are known from the state of the art.

For that purpose taking a for example 5-cornered basic shape of a gem the material regions between the rays of the star have to be removed therefrom. A complicated grinding procedure is therefore required to grind the frequently very small gems to the stellar shape.

Gems with a so-called chaton grind are also known. Such a gem is described for example in EP 2 505 096 A1.

A gem with a chaton grind has a crown, also referred to as the upper portion, with a defined number of lateral facets (crown facets) and a flat table, as well as a pavilion, also referred to as the lower portion, with a defined number of facets (pavilion facets). The end of the gem, opposite to the table, can be in the form of a point or in the form of a rounded point in the form of a so-called calette.

A so-called girdle (peripheral edge) can be arranged between the upper and lower portions. The gem may be ground symmetrically or asymmetrically.

A further parameter which is significant for the present invention is the “light return”. The light return is a measure of how much light which is incident on the gem from a pre-defined, relatively wide solid angle range, is returned to the viewer substantially along the axis of symmetry of the gem in a relatively narrow directed solid angle range (aperture angle 3°).

The light return is based on innumerable internal light reflections. Those light reflections are produced at the individual facets which are disposed relative to each other at special angle relationships characterizing the respective grind.

To calculate the light return attention is directed to EP 2 505 096 A1. The gem in accordance with EP 2 505 096 A1 has a particularly high level of light return.

The contrast between regions of the gem that appear lighter and darker is used to denote the ratio of the light return in the lighter regions less the light return in the darker regions, divided by the light return in the lighter regions. If that value is multiplied by 100 that gives the contrast in percent.

Expressed as a formula the following applies for calculation of the contrast:

contrast=(light return in the lighter regions minus the light return in the darker regions)/light return in the lighter regions.

In gems in accordance with the state of the art the aim is to achieve a uniform light return over the entire surface of the gemstone. Gems in accordance with the state of the art therefore do not have stellar appearance.

An object of the present invention is to produce a gem having a stellar appearance more economically than by producing a stellar outside contour.

That object is attained by a gem having the features of claim 1 and an arrangement having the features of claim 7.

Because the gem has a crown having a plurality of crown facets, and a first group of crown facets tapering towards a girdle has an angle α of 22.5°±3°, preferably 22.5°±2° relative to the girdle plane, and a second group of crown facets which with their wide side adjoin the girdle has an angle β of 34°±3°, preferably 34°±2° relative to the girdle plane, that affords, solely due to the pattern achieved in that way in respect of the light intensity, a stellar appearance for the gem without the removal of material that is required in the state of the art.

Advantageous embodiments of the invention are defined in the appendant claims.

Frequently gems have a pavilion arranged beneath the crown. It has been found that the above-described effect can be still further enhanced in such stones if special angles are also selected for the pavilion facets. It has proven to be particularly advantageous in that respect if the gem has a pavilion having a plurality of pavilion facets, wherein a first group of pavilion facets tapering towards the girdle has an angle of 43.5°±3°, preferably 43.5°±2° relative to the girdle plane and a second group of pavilion facets which with a wide side adjoin the girdle has an angle of 50°±3°, preferably 50°±2° relative to the girdle plane.

Basically it is provided that all pavilion and crown facets belong to the respective one or other group of facets which taper towards the girdle or which have a wide side at the girdle, with the above-mentioned angle positions, but it is also possible to envisage that there are also additional facets involving different angle positions as long as that does not substantially adversely affect the desired appearance.

In a further preferred embodiment it can be provided that in plan view the gem has a pentagonal contour.

It can further preferably be provided that the gem consists of a material transparent for the visible spectrum of light and has a refractive index of between 2.0 and 2.4.

Particularly preferably it can be provided that the gem consists of cubic zirconia.

In a further preferred embodiment it can be provided that the contrast of the light return between the first group of facets tapering towards the girdle and the second group of facets tapering towards the middle, determined in each case at a position measured radially outwardly from the longitudinal axis of the gem, of two thirds of the radius of a peripheral circumcircle extending around the contour of the gem in the respective angle bisector of the respective facet, is at least 50%.

If a setting is provided for the gem it is preferably provided that the claws of the setting which serve to fix the gem are arranged in the region of that group of facets which with their wide side adjoin the girdle. By virtue of the configuration of the facets according to the invention the gem appears darker in the region of those facets adjoining the girdle with their wide side. The stellar impression is further enhanced by the coverage of the regions of the gem, that appear darker.

Further advantages of the invention will be apparent from the Figures and the related specific description. In the Figures:

FIGS. 1a through 1g show views of an embodiment of the invention from different directions,

FIGS. 2a through 2b show views of an arrangement of the gem of FIG. 1 with a setting,

FIG. 3 shows a diagrammatic view to define the position of the facet angles,

FIG. 4 shows a diagram to illustrate the light return (“Lightreturn”) for a straight section through the gem of FIG. 5,

FIG. 5 shows a view to illustrate the position of the measurement line for the diagram of the light return in FIG. 4,

FIG. 6 shows a diagram to represent the light return for a section through the gem along the circle as shown in FIG. 7,

FIG. 7 shows a view to illustrate the position of the measurement line for the diagram of the light return in FIG. 6,

FIG. 8 shows a view to illustrate the light rays issuing from the gem for the diagram of the light return,

FIG. 9a shows a photographic representation of the appearance of a gem according to the invention, and

FIG. 9b shows a photographic representation of the appearance of a gem according to the state of the art.

FIG. 1a shows a side view of an embodiment of a gem 1 according to the invention. It is possible to see the crown 2, also referred to as the upper portion, the pavilion 3, also referred to as the lower portion, the girdle 4 and the table 5. The girdle is that region between the crown and the pavilion, at which the stone is of its largest cross-sectional extent. The girdle plane E is illustrated diagrammatically, that is that plane whose normal vector is parallel to the longitudinal axis L of the stone and in which the gem is of its largest cross-sectional extent.

FIG. 1b shows a further side view of a gem 1 according to the invention.

FIG. 1c is shows a plan view on to the crown 2 of a gem 1 according to the invention. In that respect it is possible to see two kinds of crown facets 6, 7. In this case five crown facets 6 adjoin the girdle, with their point. A further five crown facets 7 adjoin the girdle 4 with their wide side.

FIG. 1d shows a further side view of the gem 1 according to the invention.

FIG. 1e shows a plan view on to the pavilion 3 of a gem 1 according to the invention. The pavilion 3 has two kinds of pavilion facets 8, 9. In this case the pavilion facets of the group 8 adjoin the girdle with their point. Further pavilion facets of the group 9 adjoin the girdle 4 with a wide side. For the sake of clarity the drawing does not identify all facets with reference numerals.

FIG. 1f shows a perspective view on to the crown 2 of a gem 1 according to the invention.

FIG. 1g shows a further side view of a gem 1 according to the invention.

FIG. 2a shows an arrangement of a gem 1 according to the invention and a setting 10 and claw 11 in cross-section.

FIG. 2b shows a plan view of an arrangement of a gem 1 according to the invention and a setting 10. The setting is of such a configuration that the claws 11 cover the respective darker regions of the gem and thus emphasize the impression of a star. For the sake of clarity only two of the claws have reference numerals.

FIG. 3 shows a diagrammatic view of a gem 1 according to the invention for defining the angle position of the facets relative to the girdle plane E. The angle of a facet relative to the girdle plane is therefore measured between the facet which appears in projecting relationship, and the girdle plane. The angles in the Figure do not have to correspond to the values according to the invention.

FIG. 4 shows the pattern of the light return along a notional section A-B through a gem, which for comparison is in the form of a conventional gem 1 and a gem 1 according to the invention. In this case the solid-line curve shows the pattern of the light return for a conventionally ground gem while the broken-line curve shows the pattern of the light return of a gem 1 according to the invention. It will be clear that in the case of the gem 1 according to the invention the magnitude of the light return in the edge regions is substantially less than in the case of a conventionally ground gem. In other words, with the gem 1 according to the invention, the contrast between the light return in the region of one of the rays of the star and in the region between two rays of the star is greater than in the state of the art. That gives the optical impression of a star with the gem 1 according to the invention.

FIG. 5 shows the position L′ of the measurement line A-B for the diagram of the light return in FIG. 1. The measurement line is approximately at half the height of the triangle CDE, wherein the height is meant between C and the base DE.

FIG. 6 shows the pattern of the light return along a notional section E-F along a circle through a gem, which for comparison is in the form of a conventional gem and a gem 1 according to the invention. In this case the solid curve shows the pattern of the light return for a conventionally ground gem while the broken-line curve shows the pattern of the light return of a gem 1 according to the invention. It will be clear that with the gem 1 according to the invention the magnitude of the light return in the regions of the facets tapering towards the center is substantially less than in the regions of the facets tapering towards the girdle 4. In the case of the gem 1 according to the invention the light return varies azimuthally periodically thereby giving the optical impression of a star. In the case of a gem in accordance with the state of the art in contrast the light return along the notional section E-F does not exhibit any pronounced periodic changes so that no such impression occurs with the gem in accordance with the state of the art.

FIG. 7 shows the position L″ of the measurement line E-F along a circle for the diagram of the light return in FIG. 6. The measurement line E-F is on a circle centered with respect to the central axis, on a position measured from the inside outwardly at about two thirds of the radius of a circle extending around the contour of the gem (1).

FIG. 8 is a view to illustrate the light rays issuing from a gem for the diagram of the light return in FIGS. 4 and 6.

FIG. 9a shows a photographic representation of a gem 1 according to the invention. The darker regions between the axes of symmetry can be clearly seen. That gives the optical impression of a star with the gem 1 according to the invention.

FIG. 9b shows a photographic representation of a gem according to the state of the art, in which there is no optical impression of a star.

For the sake of completeness it is to be noted that in respect of angle details a full angle corresponds to 360°. 

1. A gem having a stellar appearance, wherein the gem has a crown having a plurality of crown facets, and a first group of crown facets tapering towards a girdle has an angle a of 22.5°±3°, preferably 22.5°+2° relative to the girdle plane, and a second group of crown facets which with their wide side adjoin the girdle has an angle β of 34°±3°, preferably 34°+2° relative to the girdle plane.
 2. A gem as set forth in claim 1 wherein the gem has a pavilion having a plurality of pavilion facets, wherein a first group of pavilion facets tapering towards the girdle has an angle γ of 43.5°+3°, preferably 43.5°+2° relative to the girdle plane and a second group of pavilion facets which with a wide side adjoin the girdle has an angle δ of 50°+3°, preferably 50°+2° relative to the girdle plane.
 3. A gem as set forth in claim 1, wherein in plan view the gem has a pentagonal contour.
 4. A gem as set forth in claim 1, wherein the gem consists of a material transparent for the visible spectrum of light and has a refractive index of between 2.0 and 2.4.
 5. A gem as set forth in claim 1, wherein the gem consists of cubic zirconia.
 6. A gem as set forth in claim 1, wherein the contrast of the light return between the first group of facets tapering towards the girdle and the second group of facets tapering towards the middle, determined in each case at a position measured radially outwardly from the longitudinal axis of the gem, of two thirds of the radius of a peripheral circumcircle extending around the contour of the gem in the respective angle bisector of the respective facet, is at least 50%, preferably at least 70% , particularly preferably at least 80%.
 7. An arrangement comprising: a gem, in particular as set forth in claim 1, a setting, wherein claws of the setting engage over the edge of the gem, wherein the claws are so shaped and preferably arranged in the region of the second group of crown facets that the visible surface of the gem is delimited by an alternately convex and concave edge line.
 8. An arrangement as set forth in claim 7, wherein the visible surface of the gem forms the surface of a five-ray star.
 9. A gem as set forth in claim 2, wherein in plan view the gem has a pentagonal contour.
 10. A gem as set forth in claim 2, wherein the gem consists of a material transparent for the visible spectrum of light and has a refractive index of between 2.0 and 2.4.
 11. A gem as set forth in claim 3, wherein the gem consists of a material transparent for the visible spectrum of light and has a refractive index of between 2.0 and 2.4.
 12. A gem as set forth in claim 9, wherein the gem consists of a material transparent for the visible spectrum of light and has a refractive index of between 2.0 and 2.4.
 13. A gem as set forth in claim 2, wherein the gem consists of cubic zirconia.
 14. A gem as set forth in claim 3, wherein the gem consists of cubic zirconia.
 15. A gem as set forth in claim 4, wherein the gem consists of cubic zirconia.
 16. A gem as set forth in claim 9, wherein the gem consists of cubic zirconia.
 17. A gem as set forth in claim 10, wherein the gem consists of cubic zirconia.
 18. A gem as set forth in claim 11, wherein the gem consists of cubic zirconia.
 19. A gem as set forth in claim 12, wherein the gem consists of cubic zirconia.
 20. A gem as set forth in claim 2, wherein the contrast of the light return between the first group of facets tapering towards the girdle and the second group of facets tapering towards the middle, determined in each case at a position measured radially outwardly from the longitudinal axis of the gem, of two thirds of the radius of a peripheral circumcircle extending around the contour of the gem in the respective angle bisector of the respective facet, is at least 50%, preferably at least 70% , particularly preferably at least 80%. 